A wearable display device, such as, for example, a head-mounted display (HMD), is a device that is devised to let a pilot know flight information including, for example, the altitude and speed of an airplane. General commercial products were invented in the 1990s, and commercialized products have received great attention since 1997.
A wearable display device is a device that is worn on the head, like a pair of glasses, so that an enlarged image is formed in front of the user's eyes so as to allow the user to view the image, and a display having a size of 1 inch or less is generally used therein, but the user can view an enlarged screen approaching 100 times the actual size through the application of high-grade optical technology.
The growth of the wearable computing industry is expected due to the technical development and commercialization of peripheral appliances such as wearable display devices. Although current wearable display devices have mainly been developed for the enjoyment of movies or games, owing to the higher performance and smaller size of computer systems and to the rapid development of display apparatuses, which are exemplarily represented by LCDs and LEDs and of image communication technology, wearable display devices have recently been studied and developed for use as wearable monitors, and commercialized products thereof have been launched.
Although the wearable display device market has encountered difficulty in the past due to relatively high prices, it is expected that the market will rapidly grow along with the wearable computer industry. The application fields of wearable display devices are expected to expand to industrial sites, sites for the maintenance of bulky products such as, for example, cars, airplanes, and ships, and warehouses, as well as to sports entertainment, such as car racing.
In particular, the development of processor and software technologies enables a reduction in the size of computing apparatuses, and wearable display devices are expected to be developed for use in personal-computing apparatuses, such as smart phones, rather than serving as a device that merely displays an image.
A wearable display device has a structure that enables a user to view an image of a real object, which is present in front of the user, i.e. a real image, and a playback imaginary image, i.e. a virtual image, with the naked eye. Thus, when the ambient brightness around the area on which a virtual image is projected is high, the degree to which the user visually perceives the virtual image, i.e. the visibility of the virtual image, may be low. Even when the ambient brightness around the area on which the virtual image is projected is low, the visibility may also be low.
With a reduction in the size of various electronic parts or optical elements, a wearable display device is used in various configurations, such as in a fashion capable of being worn on an observer. When a wearable display device is worn on an observer in the form of a pair of glasses or the like, the observer is capable of easily viewing a virtual image combined with the real-world environment image around the observer.
In the case of such a wearable display device configured to be worn on the observer to display a virtual image to the observer, a reduction in the size and the weight thereof is required in order to improve user convenience, and various research regarding this is in progress.